Communication System Between Electronic Devices

ABSTRACT

A system for communicating between electronic devices on a communication bus includes a communication bus and one or more communication circuits each having an output driver coupled to the communication bus and each having an input terminal. Each communication circuit produces, in response to a request message, a data communication on the communication bus in a predetermined order with respect to data communications from other communication circuits so that the data communications from each communication circuit form a sequential data stream in response to the request message.

FIELD

This disclosure relates to electronic communication and, moreparticularly, to low latency serial communication.

BACKGROUND

Serial communication protocols between electronic devices, particularlysingle-wire protocols, often include a host controller device and one ormore slave devices communicating on a common bus. Examples of suchcommunication protocols include the I²C protocol, SMBus protocol, CANprotocol, etc.

These protocols typically include a one or more host or controllerdevices that transmit requests onto the bus, and one or more slavedevices that transmit responses onto the bus. If the host device is toreceive data from multiple slave devices, the host device will send arequest to the first device that includes the first device's address.Then, after the first device response, the host sends another request tothe second device that includes the second device's address. Addressingeach slave device individually may cause undesirable latency, especiallyin applications such as automotive systems monitoring systems, which mayrequire fast response times with low latency.

SUMMARY

In an embodiment, a system includes a communication bus and one or morecommunication circuits each having an output driver coupled to thecommunication bus and each having an input terminal. Each communicationcircuit produces, in response to a request message, a data communicationon the communication bus in a predetermined order with respect to datacommunications from other communication circuits so that the datacommunications from each communication circuit form a sequential datastream in response to the request message.

One or more of the following features may be included.

The input terminals from slave communication circuits may be coupled tothe communication bus to allow the communication circuit to readmessages from the communication bus.

The input terminal and the output driver of each communication circuitmay share a common connection to the communication bus.

Two or more of the communication circuits may be situated in a samepackage.

All the communication circuits may be situated in the same package.

The input terminals may be connected to a synchronization bus to receivesynchronization signals.

The synchronization bus may be internal to a package containing one ormore of the communication circuits.

At least a portion of the synchronization bus may be external to apackage containing one or more communication circuits.

The synchronization signals may provide information to coordinate thepredetermined time order between the communication circuits, so that thedata communications from each communication circuit forms the contiguousdata stream.

The synchronization bus may be a common bus.

The synchronization bus may be a daisy-chain bus.

The communication circuits may transmit the data communications inresponse to synchronization signals received from the synchronizationbus.

The synchronization signals may be produced by one or more of thecommunication circuits.

The data stream may comprise a synchronization message before each datacommunication.

The synchronization message may be produced by a host circuit.

The synchronization message may be produced by one or more of thecommunication circuits.

One synchronization message may be produced at the beginning of the datastream.

The data stream may comprise multiple synchronization messages, eachpreceding a data communication in the data stream.

One or more of the communication circuits may produces an error checkmessage.

The error check message may be generated based on all the datacommunications in the data stream.

The error check message may follow one or more of the datacommunications in the data stream.

The error check message may be generated at the end of the data stream.

The communication circuits may communicate on the bus according to aSENT protocol.

Each communication circuit may comprise a magnetic field sensor.

The data communications from each communication circuit form atime-contiguous data stream.

In another embodiment, a communication circuit includes an output drivercoupled to a communication bus; an input terminal configured to receivea synchronization message; and communication circuitry configured toproduce, in response to a request message, a data communication on thecommunication bus in a predetermined order with respect to datacommunication from other communication circuits so that the datacommunication is generated as a portion of a sequential data stream inresponse to the request message.

One or more of the following features may be included.

The output driver and the input terminal may be coupled to the samecommunication bus.

The input terminal may be coupled to a synchronization bus.

In another embodiment, a method of communicating data from multiplecommunication circuits operating on a communication bus includestransmitting a request message on the communication bus; receiving therequest message by one or more communication circuits operating on thecommunication bus; and in response to receiving the request message,transmitting, by each of the communication circuits at a predeterminedtime, a communication message, wherein the communication messagescommunicated by the communication circuits form a sequential data streamon the communication bus.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing features may be more fully understood from the followingdescription of the drawings. The drawings aid in explaining andunderstanding the disclosed technology. Since it is often impractical orimpossible to illustrate and describe every possible embodiment, theprovided figures depict one or more exemplary embodiments. Accordingly,the figures are not intended to limit the scope of the invention. Likenumbers in the figures denote like elements.

FIG. 1 is a block diagram of a system for communicating data between amagnetic field sensor and host computer.

FIG. 2 is a block diagram of a system for communicating data between amagnetic field sensor and host computer.

FIG. 3 is a data sequence diagram of a data message for communicationover a serial bus.

FIG. 4 is a block diagram of a device that communicates serial data overa bus.

FIG. 5 is a block diagram of another embodiment of a device thatcommunicates serial data over a bus.

FIG. 6 is a block diagram of another embodiment of a device thatcommunicates serial data over bus.

FIG. 6A is a block diagram of another embodiment of a device thatcommunicates serial data over a bus.

FIG. 6B is a block diagram of another embodiment of a device thatcommunicates serial data over a bus.

FIG. 7 is a data sequence diagram of a data messages for communicationover a serial bus.

FIG. 8 is a data sequence diagram of a data messages for communicationover a serial bus.

FIG. 9 is a data sequence diagram of a data messages for communicationover a serial bus.

DETAILED DESCRIPTION

As used herein, the term “magnetic field sensing element” is used todescribe a variety of electronic elements that can sense a magneticfield. The magnetic field sensing element can be, but is not limited to,a Hall Effect element, a magnetoresistance element, or amagnetotransistor. As is known, there are different types of Hall Effectelements, for example, a planar Hall element, a vertical Hall element,and a Circular Vertical Hall (CVH) element. As is also known, there aredifferent types of magnetoresistance elements, for example, asemiconductor magnetoresistance element such as Indium Antimonide(InSb), a giant magnetoresistance (GMR) element, an anisotropicmagnetoresistance element (AMR), a tunneling magnetoresistance (TMR)element, and a magnetic tunnel junction (MTJ). The magnetic fieldsensing element may be a single element or, alternatively, may includetwo or more magnetic field sensing elements arranged in variousconfigurations, e.g., a half bridge or full (Wheatstone) bridge.Depending on the device type and other application requirements, themagnetic field sensing element may be a device made of a type IVsemiconductor material such as Silicon (Si) or Germanium (Ge), or a typeIII-V semiconductor material like Gallium-Arsenide (GaAs) or an Indiumcompound, e.g., Indium-Antimonide (InSb).

As is known, some of the above-described magnetic field sensing elementstend to have an axis of maximum sensitivity parallel to a substrate thatsupports the magnetic field sensing element, and others of theabove-described magnetic field sensing elements tend to have an axis ofmaximum sensitivity perpendicular a substrate that supports the magneticfield sensing element. In particular, planar Hall elements tend to haveaxes of sensitivity perpendicular to a substrate, while metal based ormetallic magneto resistance elements (e.g., GMR, TMR, AMR) and verticalHall elements tend to have axes of sensitivity parallel to a substrate.

As used herein, the term “magnetic field sensor” is used to describe acircuit that uses a magnetic field sensing element, generally incombination with other circuits. Magnetic field sensors are used in avariety of applications, including, but not limited to, an angle sensorthat senses an angle of a direction of a magnetic field, a currentsensor that senses a magnetic field generated by a current carried by acurrent-carrying conductor, a magnetic switch that senses the proximityof a ferromagnetic object, a rotation detector that senses passingferromagnetic articles, for example, magnetic domains of a ring magnetor a ferromagnetic target (e.g., gear teeth) where the magnetic fieldsensor is used in combination with a back-biased or other magnet, and amagnetic field sensor that senses a magnetic field density of a magneticfield.

As used herein, the terms “target” and “magnetic target” are used todescribe an object to be sensed or detected by a magnetic field sensoror magnetic field sensing element.

FIG. 1 is a block diagram of a system 100 for detecting a target 102.System 100 includes a magnetic field sensor 104 placed adjacent totarget 102 so that a magnetic field 106 can be sensed by magnetic fieldsensor 104.

In an embodiment, target 102 is a magnetic target and produces magneticfield 106. In another embodiment, magnetic field 106 is generated by amagnetic source (e.g. a back-bias magnet or electromagnet) that is notcoupled to target 102. In such embodiments, target 102 may be aferromagnetic target that does not itself tend to generate a magneticfield. In the case where the target is a ferromagnetic target, as target102 moves through or within magnetic field 106 generated by a back-biasmagnet or electromagnet, it causes perturbations to magnetic field 106that can be detected by magnetic field sensor 104.

Magnetic field sensor 104 may be coupled to a computer 108, which mayinclude a general purpose processor executing software or firmware, acustom processor, or an electronic circuit for processing output signal104 a from magnetic field sensor 104. Output signal 104 a may provideinformation about the speed and direction of target 102 to computer 108,which may then perform operations based on the received speed anddirection. In an embodiment, magnetic field sensor 104 changes the stateof output signal 104 a when the detected magnetic field crosses apredetermined threshold.

In an embodiment, computer 108 is an automotive computer installed in avehicle and target 102 is, or is coupled to, a moving part within thevehicle, such as a transmission shaft, a brake rotor, etc. Magneticfield sensor 104 detects the speed and direction of target 102 andcomputer 108 controls automotive functions (like all-wheel drive, ABS,etc.) in response to the detected speed and direction.

Target 102 can comprise any element capable of affecting magnetic field106 through motion or proximity. For example, target 102 may be attachedto a rotating shaft in an automotive transmission or brake system.

As shown in FIG. 1, target 102 may be a gear having teeth 110. As target102 moves or rotates, teeth 110 affect magnetic field 106, which can bedetected by magnetic field sensor 104. By detecting such changes tomagnetic field 106, system 100 can determine speed and/or direction oftarget 102. Although shown as a rotating gear, target 102 can take anyform capable of being detected by magnetic sensor including, but notlimited to: a toothed rack in a rack and pinion system; a gear; a gearwith teeth, with magnets (e.g., a ring magnet), or other features on orattached to a shaft; etc. Also, although shown as separate elements,computer 108 and magnetic field sensor 104 may be part of the samecircuit, part of the same integrated circuit, or contained in the samepackage.

Sensor 104 may communicate with computer 108 using a serialcommunication protocol. For example, sensor 104 may communicate using asingle-line protocol, such as the SENT protocol, the I²C protocol, orthe like. In this case, signal 104 a may travel on a single wire. Inother embodiments, other protocols may be used and signal 104 a maytravel over a differential wire or a bus.

Referring to FIG. 2, system 200 may include computer 202, which may bethe same as or similar to computer 108. Computer 202 may communicatewith electronic device 204 over communication bus 206. Communication bus206 may be a serial communication bus comprising one or more wires. Inembodiments, computer 202 and electronic device 204 may communicate overbus 206 using a protocol that is the same as or similar to the SENTprotocol, the I²C protocol, or another single-wire protocol.

Electronic device 204 may comprise one or more circuits 208-214 thatgenerate data to be communicated to computer 202. Each circuit mayinclude a receiver, transmitter, or transceiver circuit coupled to bus206 that provides each circuit with the functionality to drive andcommunicate on bus 206. For example, circuits 208-214 may be magneticfield sensors in a motor vehicle that collect data about the operationof the motor vehicle.

Circuits 208-214 may be integrated circuits, some or all of which aresupported by a separate die in the same or in a separate integratedcircuit package. Alternatively, some or all of circuits 208-214 may besupported on the same die. Electronic device 204 may comprise a numberof disparate circuits (e.g. circuit 208-214) that are communicativelycoupled to bus 206 and can coordinate communication of data across bus206 among themselves. For example, electronic device 204 may be fourbrake rotor rotation sensors, each located at a different wheel of avehicle, that can coordinate communication over bus 206. Although fourcircuits 208-214 are shown, electronic device 204 may include anyarbitrary number of circuits for communicating on bus 206.

FIG. 3 is a diagram 300 of data communicated across bus 206. Thehorizontal axis of diagram 300 represents time. In this example, thecommunication sequence begins with a so-called “pause pulse” 302 wherebus 206 is idle. Computer 202 may then send a request 304 for data fromelectronic device 204 by, for example, driving a voltage on bus 206 lowfor a specified amount of time. Electronic device 204 may answer therequest by sending response 306, which may include an aggregation ofdata from more than one of circuits 208-214. For example, data unit 308may include data from circuit 208, data unit 310 may include data fromcircuit 210, etc. Circuits 208-214 may communicate and coordinate witheach other so that each circuit 208-214 drives its own data onto bus 206in a predetermined sequence to form message 306.

Referring to FIG. 4, circuits 208-214 may be coupled to a communicationbus 402, which may be a one-wire bus. In an embodiment, circuits 208-214and bus 402 may be internal to electronic device 204. For example,circuits 208-214 and bus 402 may be enclosed in the same electronicdevice package. Bus 402 may be coupled to bus 206 through pin 404, whichmay be a pin, ball, bond pad, or other type of electrical access pointthat permits electrical connection to circuits within the electronicdevice package.

Each circuit 208-214 may use a transceiver to read and write data to bus402. For example, when a request for data is sent (e.g. request 304 inFIG. 3), circuits 208-214 may each receive the request. Circuits 208-214may then coordinate their responses so that they form a predeterminedsequence of responses. In one example, circuit 208 may transmit dataunit 308 onto the bus. When circuit 210 reads the bus and discovers dataunit 308 has been sent, circuit 210 may then transmit data unit 310 ontothe bus. When circuit 212 reads the bus and discovers data unit 310 hasbeen sent, circuit 212 may transmit its data packet, etc. In thisexample, each circuit 208-214 contains information about when it shouldtransmit its data. For example, each circuit may include a sequencenumber (e.g. an address) that its data will appear in the resultingmessage. Circuit 208 may be configured to transmit first, circuit 210 totransmit second, circuit 212 to transmit third, etc. Thus, circuit 208may include the sequence number 0 indicating that its data will betransmitted first, circuit 210 may include the sequence number 1indicating its data will be transmitted next, etc. Each circuit readsthe bus, counts the number of data units sent, and inserts its data unitonto the bus at the appropriate time to generate a sequential stream ofdata.

Referring to 5, in another embodiment, an electronic device 204′ may besimilar to electronic device 204, and communication circuits 208′-214′may be similar to communication circuits 208-214. Electronic device 204′may include an internal synchronization bus 502 to synchronizetransmission of data units by the communication circuits 208′-214′. Inthis example, bus 502 may be a shared, or common, bus that can bewritten to and read from by each circuit 208′-214′. Thus, circuits208′-214′ may drive signals onto and read signals from synchronizationbus 502 during communication. The circuits that are not currentlydriving a signal onto bus 502 may read the signals transmitted by theother circuits. In embodiments, synchronization bus 502 may be a serialbus or a parallel bus.

In one example, each circuit 208′-214′ drives a signal ontosynchronization bus 502 to indicate transmission of a data unit, by therespective circuit, onto bus 402. For example, circuit 208′ may drive asignal onto bus 502 to indicate transmission of data unit 308, circuit210′ may drive a signal onto bus 502 to indicate transmission of dataunit 310, etc. Each circuit may drive the signal onto bus 502 at thebeginning of, the end of, or during transmission of the data packet. Thesignal may be a simple logic bit (e.g. a high or low voltage driven ontobus 502), a series of bits driven serially, or a series of bits drivenin parallel (in the case that bus 502 is a parallel bus). In oneexample, the circuits may transmit the signal by pulling bus 502 to alow voltage for the duration of the time that they transmit data ontobus 402. When the bus is released, the next circuit can drive bus 502low and transmit its data onto bus 402.

Each circuit may also transmit its sequence number onto synchronizationbus 502. For example, at the end of its transmission, circuit 208 maytransmit its sequence number ‘0’ onto bus 502. The other circuits mayreceive this transmission as acknowledgment that circuit 208 completedits transmission. In response, the next circuit in the sequence maytransmit its data onto bus 402, and transmit its sequence number ‘1’onto synchronization bus 502 to indicate that it completed itstransmission. This process may continue until all the communicationcircuits have transmitted their data units onto bus 502.

The other circuits (i.e. the circuits that are not driving a data packetonto bus 402) may read the signal on bus 502 to determine when theyshould transmit their data packets. In one embodiment, circuits208′-214′ may count the number of logic signals to determine when theyshould transmit. For example, if circuit 214′ is to transmit fourth inthe sequence, circuit 214′ may count the number of signals driven ontobus 502 by circuits 208′, 210′, and 212′. After circuit 214′ countsthree signals driven to bus 502 indicating that three data units havebeen transmitted to bus 402, circuit 214′ may transmit its data unit inthe fourth position in the sequence. If circuit 214′ is the last circuitin the sequence, it may not need to trans its own signal onto bus 502.However, in other embodiments, circuit 214′ may transmit its own signalonto bus 502, even if it is the last circuit in the sequence, to informthe other circuits that the last data unit was transmitted. The othercircuits may then perform post transmission processing, if needed.

Referring to FIG. 6, in another embodiment, electronic device 204″ maybe similar to electronic device 204 and 204′, and circuits 208″-214″ maybe similar to circuits 208-214 and 2-9′-214′.

Electronic device 204″ may include a daisy-chained synchronization busbetween circuits 208″-214″. The daisy-chained synchronization bus mayinclude one or more direct, point-to-point connections between circuits208″-214″, such as bus 602 between circuit 208″ and 210″, bus 604between circuit 210″ and 212″, and bus 606 between circuit 212″ and214″. The circuit 208″-214″ may include a receiver to receive a signalfrom one of the daisy-chained busses, and a transmitter to transmit asignal on another of the daisy-chained busses.

In operation, each circuit 208″-214″ will transmit a signal on adaisy-chained bus to synchronize transmission with the next circuit. Forexample, circuit 208″ may transmit a signal onto bus 602 to indicatethat it has transmitted data unit 308 onto bus 402. Circuit 210″ mayreceive the signal on bus 602, which may trigger circuit 210″ tosubsequently transmit data unit 310 onto bus 402. Circuit 210″ may thentransmit a signal on bus 604 indicating that data unit 310 has beentransmitted. Circuit 212″ may receive the signal on bus 604, which maytrigger circuit 212″ to send its data unit onto bus 402, etc. This maycontinue until all the circuits 208″-214″ have transmitted their dataunits onto bus 402 to form message 306.

Although not shown, electronic device 204″ may have an additionaldaisy-chained bus between circuit 214″ and circuit 208″ to make acomplete daisy-chain circle between the circuits 208″-214″. This allowsany arbitrary circuit in the daisy-chain to be configured as the firstcircuit to transmit.

Referring to FIG, 6A, in another embodiment, electronic device 204A maybe similar to electronic device 204, 204′, and 204″, and circuits208A-214A may be similar to circuits 208-214, 208′-214′, and 208″-214″.

Electronic device 204A may include a daisy-chained synchronization busbetween circuits 208A-214A. The daisy-chained synchronization bus mayinclude one or more direct, point-to-point connections between circuits208A-214A, such as bus 602A between circuit 208A and 210A, bus 604Abetween circuit 210A and 212A, and bus 606A between circuit 212A and214A. The circuits 208A-214A may include a receiver to receive a signalfrom one of the daisy-chained busses, and a transmitter to transmit asignal on another of the daisy-chained busses.

In operation, circuit 208A may receive request signal on bus 608. Inresponse, circuit 208A may send a signal to circuit 210A via daisy-chainbus 602A indicating that a request for data was received. Circuits 210A,212A, 214A may relay the request along daisy-chain busses 604A and 606Auntil all the circuits have received and are aware of the request signalreceived on bus 608.

Subsequently, each circuit 208A-214A will transmit a signal and dataonto the daisy-chained bus to synchronize transmission with the nextcircuit. For example, circuit 214A may transmit its data to circuit 212Avia bus 606A. Circuit 212A may append its data to the data it receivedfrom circuit 214A, and transmit the resulting data to circuit 210A viabus 604A. Circuit 214A may append its data to the data it received fromcircuit 212A, and transmit the resulting data to circuit 208A via bus602A. Circuit 208A may append its data to the data received from circuit210A. Because circuit 208A is the last circuit in the daisy chain,circuit 208A may calculate and append any error codes to the data, andtransmit the resulting packet out onto output line 608. A computingdevice coupled to output line 608 may receive the packet for subsequentprocessing.

Although not shown, electronic device 204″ may have an additionaldaisy-chained bus between circuit 214″ and circuit 208″ to make acomplete daisy-chain circle between the circuits 208″-214″. This allowsany arbitrary circuit in the daisy-chain to be configured as the firstcircuit to transmit.

Referring to FIG. 6B, in another embodiment, an electronic device 204Bmay be similar to the electronic devices 204, 204′, 204″, and/or 204Adescribed above, and communication circuits 208B-214B may be similar tothe communication circuits described above.

Electronic device 204B may include an internal synchronization bus 502Bto synchronize transmission of data units by the communication circuits208B-214B. In this example, bus 502B may be a shared, or common, busthat can be written to and read from by each circuit 208B-214B. Thus,circuits 208B-214B may drive signals onto and read signals fromsynchronization bus 502B during communication. The circuits that are notcurrently driving a signal onto bus 502B may read the signalstransmitted by the other circuits. In embodiments, synchronization bus502B may be a serial bus or a parallel bus.

In one example, circuit 208B may receive a request for data signal onbus 610. Subsequently, circuit 208B may transmit a signal ontosynchronization bus 502B, informing circuits 210B-214B of the requestfor data received on bus 610.

Subsequently, each circuit 208B-214B may drive data on synchronizationbus 502B. Each circuit may also drive a signal onto synchronization bus502B to indicate an end of transmission onto bus 502B by the respectivecircuit. For example, circuit 214B may drive data unit 308 onto bus502B. Circuit 210B may drive data unit 310 onto bus 502B, etc. Eachcircuit may also drive a signal onto bus 502B at the beginning or end ofdriving a data unit in order to negotiate data transmission on theshared bus 502B.

One or more of the circuits may aggregate the data into message 306. Forexample, circuit 208B may aggregate the data units received from theother circuits and append its own data unit to message 306. Then,circuit 208B may transmit the message 306 (and any requiredcommunication protocol elements such as pause pulse 302 and/or request304) onto bus 610.

In other embodiments, each communication circuit may aggregate its owndata unit to the message, then transmit the message into shared bus502B. For example, circuit 214B may transmit data unit 308 onto bus502B. Circuit 212B may receive data unit 308 and append data unit 310 toit. Circuit 212B may then transmit both data unit 308 and 310 onto bus502B. This process may continue, each circuit adding its own data unitto the growing packet, until packet 306 is fully formed. At that point,circuit 208B may transmit the fully formed packet 306 onto bus 610.

Each circuit may also transmit its sequence number onto synchronizationbus 502B. For example, at the end of its transmission, circuit 208B maytransmit its sequence number ‘0’ onto bus 502B. The other circuits mayreceive this transmission as acknowledgment that circuit 208B completedits transmission. In response, the next circuit in the sequence maytransmit its data onto bus 502B and transmit its sequence number ‘1’onto synchronization bus 502B to indicate that it completed itstransmission. This process may continue until all the communicationcircuits have transmitted their data units onto bus 502B.

The other circuits (i.e. the circuits that are not driving a data packetonto bus 502B) may read the signal on bus 502B to determine when theyshould transmit their data packets. In one embodiment, circuits208B-214B may count the number of logic signals to determine when theyshould transmit. For example, if circuit 214B is to transmit fourth inthe sequence, circuit 214B may count the number of signals driven ontobus 502B by circuits 208B, 210B, and 212B. After circuit 214B countsthree signals driven to bus 502B indicating that three data units havebeen transmitted to bus 502B, circuit 214B may transmit its data unit inthe fourth position in the sequence. If circuit 214B is the last circuitin the sequence, it may not need to transmit its own signal onto bus502B. However, in other embodiments, circuit 214B may transmit its ownsignal onto bus 502B, even if it is the last circuit in the sequence, toinform the other circuits that the last data unit was transmitted. Theother circuits may then perform post transmission processing, if needed.

FIG. 7-FIG. 9 illustrate additional examples of data streams messagesequences) sent by the communication circuits.

Data stream 700 begins with a request 702 from a host computer (e.g.computer 202 in FIG. 2). The host computer or one of the communicationcircuits 208-214 may then transmit a synchronization bit pattern 704 sothat all the devices communicating on the bus can synchronize theirrespective clocks for transmitting and receiving serial data. A serialcommunication nibble (SCN) 706 containing information about thecommunication network and/or the data stream may be transmitted next bythe host computer or one of the communication circuits. After SCN 706,circuit 208 may transmit its data unit 708. In embodiments, circuit 208may also transmit an error pattern 710, which may be a CRC check, aparity bit, or any other type of error checking or correcting code.

When communication circuit 208 completes its transmission, circuit 210may initiate its transmission by transmitting its own SCN 712, its dataunit 711, and another error pattern 716. The other communicationcircuits may follow suit, transmitting their data in a predeterminedorder, until data stream 700 is complete. In this way, data stream 700may include an SCN that precedes each data unit and an error sequencethat follows each data unit. Synchronization between the communicationcircuits 208-214 may occur in any of the ways described above including,but not limited to, each circuit reading the transmissions, a commonsynchronization bus, a daisy-chained synchronization bus, etc.

Data stream 800 in FIG. 8 may include a single SCN and a single CRC.Data stream 800 begins with a request 802 from a host computer (e.g.computer 202 in FIG. 2). The host computer or one of the communicationcircuits 208-214 may then transmit a synchronization bit pattern 804 sothat all the devices communicating on the bus can synchronize theirrespective clocks for transmitting and receiving serial data. A serialcommunication nibble (SCN) 806 containing information about thecommunication network and/or the data stream may be transmitted next bythe host computer or one of the communication circuits. After SCN 806,circuit 208 may transmit its data unit 808, followed by data unit 810transmitted by circuit 210, data unit 812 transmitted by circuit 212,and data unit 814 transmitted by circuit 214. During transmission, oneof the communication circuits 208-214 may calculate an error code 816,such as CRC value and transmit the error code after the data units havebeen transmitted. Error code 816 may be calculated based on any or allof the preceding data units 808-812.

Data stream 900 in FIG. 9 may include a single SCN and a single CRC, aswell as one or more error data units. Data stream 900 begins with arequest 902 from a host computer (e.g. computer 202 in FIG. 2). The hostcomputer or one of the communication circuits 208-214 may then transmita synchronization bit pattern 904 so that all the devices communicatingon the bus can synchronize their respective clocks for transmitting andreceiving serial data. A serial communication nibble (SCN) 906containing information about the communication network and/or the datastream may be transmitted next by the host computer or one of thecommunication circuits. After SCN 906, circuit 208 may transmit its dataunit 908, followed by data unit 910 transmitted by circuit 210, and dataunits from the other communication circuits. After the data units havebeen transmitted, one or more of the communication circuits may transmiterror data units 912 and 914. These data units may contain error codesthat are useful to the host computer. For example, if circuits 208-214are magnetic field sensors, the error data units 912, 914 may containerror codes relating to operation of the magnetic field sensors ordetection of the magnetic field. During transmission, one of thecommunication circuits 208-214 may calculate an error code 916, such asCRC value and transmit the error code after the data units and errordata units 912, 914 have been transmitted. Error code 916 may becalculated based on any or all of the preceding data units and errordata units transmitted on the bus.

In embodiments, the final communication circuit to process the data unitmay generate the error code. For example, if communication circuit 208″(see FIG. 6) is the last communication circuit in the daisy-chain toprocess the data unit, then communication circuit 208″ may calculateerror code 912, 914 and/or CRC 916.

Having described preferred embodiments, which serve to illustratevarious concepts, structures and techniques, which are the subject ofthis patent, it will now become apparent to those of ordinary skill inthe art that other embodiments incorporating these concepts, structuresand techniques may be used. Accordingly, it is submitted that that scopeof the patent should not be limited to the described embodiments butrather should be limited only by the spirit and scope of the followingclaims. All references cited in this document are incorporated byreference in their entirety.

1. A system comprising: a communication bus; a plurality ofcommunication circuits each having an output driver coupled to thecommunication bus and each having an input terminal; and asynchronization bus, wherein the input terminals are connected to thesynchronization bus to receive synchronization signals, wherein eachcommunication circuit produces, in response to a request message, a datacommunication on the communication bus in a predetermined order withrespect to data communications from other communication circuits so thatthe data communications from each communication circuit form asequential data stream in response to the request message.
 2. The systemof claim 1 wherein the input terminals are coupled to the communicationbus to allow the communication circuit to read messages from thecommunication bus.
 3. The system of claim 2 wherein the input terminaland the output driver of each communication circuit share a commonconnection to the communication bus.
 4. The system of claim 1 whereintwo or more of the communication circuits are situated in a samepackage.
 5. The system of claim 4 wherein all the communication circuitsare situated in the same package.
 6. (canceled)
 7. The system of claim 1wherein the synchronization bus is internal to a package containing oneor more of the communication circuits.
 8. The system of claim 1 whereinat least a portion of the synchronization bus is external to a packagecontaining one or more communication circuits.
 9. The system of claim 1wherein the synchronization signals provide information to coordinatethe predetermined time order between the communication circuits, so thatthe data communications from each communication circuit forms thecontiguous data stream.
 10. The system of claim 1 wherein thesynchronization bus is a common bus.
 11. The system of claim 1 whereinthe synchronization bus is a daisy-chain bus.
 12. The system of claim 1wherein the communication circuits transmit the data communications inresponse to synchronization signals received from the synchronizationbus.
 13. The system of claim 1 wherein the synchronization signals areproduced by one or more of the communication circuits.
 14. A systemcomprising: a communication bus; a plurality of communication circuitseach having an output driver coupled to the communication bus and eachhaving an input terminal, a synchronization bus, wherein the inputterminals are connected to the synchronization bus to receivesynchronization signals; wherein each communication circuit produces, inresponse to a request message, a data communication on the communicationbus in a predetermined order with respect to data communications fromother communication circuits so that the data communications from eachcommunication circuit form a sequential data stream in response to therequest, wherein the data stream comprises a synchronization messagebefore each data communication.
 15. The system of claim 14 wherein thesynchronization message is produced by a host circuit.
 16. The system ofclaim 14 wherein the synchronization message is produced by one or moreof the communication circuits.
 17. The system of claim 16 wherein onesynchronization message is produced at the beginning of the data stream.18. The system of claim 16 wherein the data stream comprises multiplesynchronization messages, each preceding a data communication in thedata stream.
 19. The system of claim 1 wherein one or more of thecommunication circuits produces an error check message.
 20. The systemof claim 19 wherein the error check message is generated based on allthe data communications in the data stream.
 21. The system of claim 20wherein the error check message follows one or more of the datacommunications in the data stream.
 22. The system of claim 21 whereinthe error check message is generated at the end of the data stream. 23.The system of claim 1 wherein the communication circuits communicate onthe bus according to a SENT protocol.
 24. The system of claim 1 whereineach communication circuit comprises a magnetic field sensor.
 25. Thesystem of claim 1 wherein the data communications from eachcommunication circuit form a time-contiguous data stream.
 26. Acommunication circuit comprising: an output driver coupled to acommunication bus; an input terminal configured to receive asynchronization message; and communication circuitry configured to:produce, in response to a request message, a data communication on thecommunication bus in a predetermined order with respect to datacommunication from other communication circuits so that the datacommunication is generated as a portion of a sequential data stream inresponse to the request message; and synchronize the data communicationwith respect to the data communication from other communication circuitsin response to the synchronization message received at the inputterminal.
 27. The communication circuit of claim 26 wherein the outputdriver and the input terminal are coupled to the same communication bus.28. The communication circuit of claim 26 wherein the input terminal iscoupled to a synchronization bus.
 29. A method of communicating datafrom multiple communication circuits operating on a communication bus,the method comprising: transmitting a request message on thecommunication bus; receiving the request message by one or morecommunication circuits operating on the communication bus; receiving bythe one or more communication circuits, at least one synchronizationsignal to synchronize responses of the one or more communicationcircuits; and in response to receiving the request message,transmitting, by each of the communication circuits, in response to theat least on synchronization signal, at a predetermined time, acommunication message, wherein the communication messages communicatedby the communication circuits form a sequential data stream on thecommunication bus.